Parallelogram-type and other types of wheelchair lifts are well known and include an outboard barrier (i.e., rollstop) for preventing a wheelchair occupant from accidentally falling from the lift platform, particularly when it is raised above ground elevation. Similarly, many lifts also include an inboard barrier which additionally prevents the wheelchair and occupant from inadvertently rolling or sliding off the inboard edge (vehicle side) of the platform and becoming trapped between the lift platform and the vehicle structure.
Such lifts employ various mechanisms to cause the inboard and outboard barriers to move in an automatic or otherwise coordinated manner relative or in response to the platform state (e.g., raising, lowering, etc.) or position. One example of a mechanism for actuating the inboard barrier is the cam actuated cable system of U.S. Pat. No. 5,605,431 to Saucier et al. This system employs a bell crank and cable wherein the lifting parallelogram actuates a cable, the length of which is controlled by a cam assembly pivoted to the lifting end link of an arm of the parallelogram. As the platform moves, the inboard barrier is raised or lowered by the other end of the cable.
Wheelchair lifts have also employed a system or assembly of linkage members, such as arms, to move and synchronize the inboard barrier relative to the lift platform elevation. One such wheelchair lift is disclosed in U.S. Pat. No. 6,238,169 to Dupuy et al. for “Dual Function Inboard Barrier/Bridgeplate Assembly For Wheelchair Lifts”, issued May 29, 2001 to applicant's assignee which is incorporated by reference herein in its entirety. The disclosed lift has a stowable platform and a dual-function safety barrier pivotably coupled thereto. The barrier is actuated by a linkage system for movement between a raised safety position and a lowered bridging position in synchronism with the elevation of the platform. The lift employs a linkage system having a slide block for pivoting the platform from the horizontal transfer position to a generally vertical stowed position. In operation, the slide block of the linkage system contacts the lower parallelogram arm during platform lifting so that a push arm of the linkage system is moved downwardly. A link, which couples the push arm to the barrier, pivots to rotate the barrier from a raised position to a substantially horizontal position to act as a bridge plate at the transfer level.
While the barrier-actuating link is particularly adept at positioning the inboard barrier, a need may also exist to ensure that the inboard barrier is retained in a desired position, particularly in its raised position. To that end, National Highway Traffic Safety Administration (NHTSA) rules require a lift interlock to inhibit raising and lowering of the lift platform unless the inboard barrier is properly positioned. Moreover, NHTSA requires that the inboard barrier be substantially rigid to prevent a wheelchair and/or wheelchair occupant on the lift platform from contacting any other structure (e.g., the vehicle).
Therefore, in view of the foregoing, it is desirable to lock the inboard barrier in a generally vertical position so that the inboard barrier poses a substantially rigid obstacle, and so that operation of the lift is not interrupted due to momentary and/or accidental contact with the inboard barrier.